Reactivity-selectivity relationships. Part 12. Intermediates formed in the solvolysis of substituted benzyl derivatives. The importance of HOMO-LUMO interactions in determining selectivity

The intermediates undergoing nucleophilic attack during the solvolysis of a series of substituted benzyl derivatives in aqueous ethanol are examined in the presence of m-chloroaniline. Conclusions are based on the measurement of substrate selectivity towards the competing nucleophiles, ethanol and m-chloroaniline and the application of perturbation molecular orbital (PMO) theory. The results suggest that p-chlorobenzyl, benzyl, and p-methyl benzyl chlorides undergo nucleophilic attack on intimate ion pairs while p-methoxybenzyl chloride undergoes attack on solvent separated ion pairs. These conclusions are in accord with a previous study on benzyl derivatives utilizing ethanol and water as competing nucleophiles. The importance of HOMO-LUMO interactions in determining substrate selectivity in nucleophilic substitution reactions, using two dissimilar nucleophiles, is confirmed.